if you have vacum at the axel, you want to check the acavator if it is ok then you may have ware to the axel and gear on the pas side. It could be worn fork, pads, or bushing on the end or the outer axel inside. I have had the same problem on several trucks 95, 97, and 98. Most of the time had to replace axel, gear, and bushing to take care of the probelm. Have goten them from a junk yard with low milage.